The invention relates to an expansion lance.
An expansion lance of the generic type is known from DE 37 16 986 A1 (corresponding to U.S. Pat. No. 5,054,756). In this case, a rod-shaped seal carrier has a sealing arrangement pushed onto it. (FIG. 2), the said sealing arrangement comprising spacer sleeves, pairs of sealing rings and intermediate sleeves, the latter being arranged between the sealing rings of the pairs. The sealing rings are supported on the other hand against the spacer sleeves or an end stop. In the case of an expansion lance of this type, in which, in the position in which it has been pushed into a pipe to be expanded, the sealing rings bear against the inside of the pipe with prestress, the sealing rings are pressed into the gap between the spacer sleeves adjoining the sealing rings, or the end stop, and the pipe when a high internal pressure is applied, intended to bring about a partial expansion of the pipe, after which the respective ring undergoes extrusion through the gap. This causes irreparable damage to the ring, which may lead immediately to leakage of the sealing arrangement. What is quite sure, however, is that the extruded ring must be exchanged before a subsequent expanding process is carried out by means of the expansion lance, so there can be no question of the expansion lance being capable of being used over long periods. FIGS. 5a and 6a of the document show versions of the sealing arrangement in which the sealing rings in the form of O-rings are placed in receiving grooves, the O-rings having to be stretched over a special spacer sleeve to assume their intended place. Furthermore, although the O-rings have supporting elements on the side facing away from the expansion location, there is a gap both between the supporting element and the pipe to be expanded and between the latter and the O-ring, as a result of which no sealing effect exists during the build-up of the high internal pressure via the gap. Although under high internal pressure the O-ring is deformed until it bears against the inside of the pipe, the ring is squeezed into the gap between the supporting element and the pipe in spite of the support (FIG. 5a). In this case, extrusion of the ring through the gap likewise occurs to a certain extent. In the version of FIG. 6a, the supporting ring itself may be extruded, after which the O-ring is extruded. Consequently, the expansion lance cannot be used over long periods. This similarly applies to the versions of FIGS. 7 and 8, the O-rings not primarily having a sealing function here but instead serving as pressure transferring means for the supporting element and being intended to press the latter against the inside of the pipe for applying the sealing effect. In this case, however, the admission pressure in the region 9 must be just as great as the joining pressure in the expansion region, since otherwise the O-ring is pressed into the bore lying thereunder. If the joining pressure is greater, the bore under the O-ring acts like a punching ring, which destroys the O-ring. If there is pressure equalisation, at the customary rates of pressure increase of approximately 2000 bar/sec the bore under the O-ring acts like a nozzle, which blasts the O-ring with the pressurized fluid. Since the supporting element is subjected directly to the pressure medium and the force resulting from the two compressive forces has an axial component, the supporting element may either easily jam in the gap between the spacer sleeve and the hollow profile or even be extruded into it.
The invention is based on the object of providing an expansion lance that can be used over long periods while ensuring a reliable sealing effect of the sealing arrangement.
The object is achieved according to the features of the present invention.
Thanks to the invention, the sealing arrangement of the expansion lance has a priori as a result of the oversize of the elastomer sealing ring with respect to the inside diameter of the hollow profile to be partially expanded an adequate sealing effect during the pressure build-up phase. In this case, the low- abrasion material of the sealing ring contributes significantly to ensuring that the expansion lance can be used over long periods. On account of the axially immovable stop, when there is full expansion pressure the elastomer ring is axially compressed, after which the axially unyielding, but radially elastic supporting ring is radially expanded by the radially swelling shoulder until it is pressed against the inside of the hollow profile. There is accordingly no gap between the hollow profile and the sealing ring into which the elastomer ring could flow, i.e. be extruded, thereby avoiding sealing damage and consequently consolidating the long-term service life of the expansion lance. The elastomer ring cannot flow away at any other point either, since its shoulder is always enclosed by the supporting ring, the seal carrier and the stop. At the same time, the fact that the elastomer ring does not flow away ensures the sealing effect during the expansion of the hollow profile subjected to high internal pressure.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.